Recommendation of the Excellence Action Plan for Chinese Science and Technology Journals: Chinese Journal of Geophysics, No. 7, 2024

Space physics · atmospheric physics and geodesy ·

Experimental study of stimulated electromagnetic radiation in the polar region

Liang Chen, Jutao Yang, Linglei He, Qingliang Li, Shuji Hao, Guanglin Ma, Yubo Yan, Haiqin Che, Yongyong Liang, Haiying Li, Wenchao Zhang

2024, 67(7): 2487-2495. doi: 10.6038/cjg2024R0524

Abstract:The complex spectral characteristics of stimulated electromagnetic emissions (SEE) provide a powerful research method for studying the physical mechanism of ionospheric heating. Based on the SEE data during the ionospheric heating experiments carried out by mainland scholars using the EISCAT heating system in 2017 and 2022, this paper analyzes the effects of polarization, frequency, power and beam direction of heating electromagnetic waves on the characteristics of SEE spectral lines, and the results show that: (1) Compared with unusual waves, the heating waves are ordinary waves during the experiments and it is easier to observe the rich SEE spectral line structures, such as the maximum value of the upshifted maximum component (UM), thermal narrow continuum (NCth) and downshifted maximum (DM), etc.; (2) The heating frequency increases from 4.07 MHz to 4.10 MHz, and the downshifted peak (DP) frequency shift is strongly linearly correlated with the heating frequency. Therefore, combined with the characteristics of DP and DM spectra during ionospheric heating, the electron cyclotron frequency in the heating region can be quickly estimated in real time. (3) The heating power increases from 24 MW to 192 MW, and a new type of downward shift spectrum feature emerges between DM and heating frequency, that is, the intermediate downshifted maximum (IDM). (4) Combined with the joint detection of ultra-high frequency incoherent scattering radar, it is found that when the heating beam is directed at a counterclockwise angle of 6° in the vertical direction, it is easier to excite the density pure growth mode of oscillating dual-flow instability, and more artificial density inhomogeneity is formed, so as to obtain stronger DM spectral lines.

Based on the FY-3D ionospheric photometer data, the response characteristics of 135.6 nm glow radiation intensity to the equatorial ring current index Dst at night were studied

Jiang Fang, Mao Tian, Fu Liping, Wang Jinsong, Hu Xiuqing, Jia Nan, Wang Tianfang, Li Yefei

2024, 67(7): 2496-2505. doi: 10.6038/cjg2023R0187

Abstract:The far-ultraviolet glow detector small ionospheric photometer IPM was launched with the FY-3D satellite on November 15, 2017.IPM can obtain the peak ionospheric electron density, total electron content, and the column density ratio of atmospheric oxygen atoms and nitrogen molecules O/N₂ during the day by measuring the glow radiation of 135.6 nm and N₂ LBH bbs generated by photoelectron excitation at night. In this paper, based on the IPM night side data, the relative variation of radiation intensity in the 135.6 nm band during magnetic storms and magnetic calm in the middle and low latitudes of the non-aurora region is studied. The results show that the radiation intensity in the 135.6 nm band is very susceptible to the disturbance of magnetic storms, and is very sensitive to the response of Dst index, even in weak magnetic storms, the radiation intensity in the 135.6 nm band will be enhanced, and the time of radiation enhancement has a good correspondence with the main phase and recovery phase of the magnetic storm. The TEC comparison with the International GNSS Service (IGS) shows that the 135.6 nm radiation enhancement during a magnetic storm is not only caused by the radiation contribution generated by the O⁺ and electron radiation recombination mechanism that is positively correlated with the ionospheric electron density information. The study of magnetic storm events of different intensities shows that the increase of 135.6 nm radiation intensity during a magnetic storm is inversely proportional to the Dst index, that is, the lower the Dst index, the greater the increase of 135.6 nm radiation intensity, and the higher the latitude, the greater the increase of 135.6 nm radiation intensity.

Variation of spin-free component of ionospheric equivalent current in the polar region during magnetic storms1

Ge Panze, Li Huijun, Cheng Wei, Huang Yingying, Wang Chengzhi

2024, 67(7): 2506-2518. doi: 10.6038/cjg2023R0046

Abstract:The ionospheric conductivity distribution in the polar region changes during a magnetic storm, resulting in complex changes in the current loop formed by the spin-free component of field current and ionospheric current. The equivalent ionospheric current in the polar region is obtained by geomagnetic inversion, which is helpful to analyze the variation law of the above current loop during magnetic storms. In this paper, the low-rank approximation method is used to invert the magnetic disturbance observation data of the polar INTERMAGNET geomagnetic network, and the equivalent current information of the ionosphere in the polar region during the two typical magnetic storms on September 20 and November 30, 2015 is obtained, and the variation of the spin-free component during the magnetic storm is investigated. The main conclusions are as follows: the ionospheric equivalent current includes passive components and spin-free components, and the passive components dominate during magnetic storms, and the proportion of spin-free components is small. At the beginning of the magnetic storm, the source of geomagnetic field disturbance mainly comes from the magnetopause, and the ionospheric current does not change significantly. In the main phase stage of magnetic storms, the passive component of the ionospheric equivalent current in the polar region exhibits a double-vortex structure, which is consistent with previous studies, while the spin-free component mainly flows from the morning side to the dusk side. In the recovery phase, the geomagnetic activity in the polar region weakens, the double-vortex structure of the passive component of the equivalent current evolves, and the current component of the spin-free component increases from the day side to the night side. The spin-free component of the equivalent current in the later stage of the recovery phase mainly flows from the dim side to the morning side, and the flow direction is opposite to that of the main phase. The change of the flow direction of the spin-free current can reflect the overall flow direction of the closed current in the ionosphere, and the reversal of the flow direction may be affected by the change of the field current.

Modeling of equatorial electrical catchment during geomagnetic calm periods

Wen Xin, Zhou Yunliang, Xiong Chao

2024, 67(7): 2519-2527. doi: 10.6038/cjg2024R0714

Abstract:In this paper, we use the Equatorial Electrojet (EEJ) data observed by the Swarm-A satellite from November 2013 to February 2023 in the past ten years, and select the peak current density of EEJ during the calm of geomagnetic activity (Kp ≤3) as the research object, and construct an empirical model of EEJ with longitude, local time, season, solar radiation flux and moon phase as parameters. Comparing the EEJ calculated by the model with the EEJ measured by the Swarm-A satellite used for the above modeling, it is found that the correlation coefficient between the two is about 0.76, and the mean absolute error (root mean square error) is about 20.91 (27.32) mA·m⁻¹. EEJ has obvious diurnal variation characteristics, with a peak at noon and a reverse EEJ near sunrise. The EEJ exhibits a significant wave-like structure with longitude. The seasonal variation characteristics of EEJ were obvious, with a peak near the equinoxical season and a trough near the second to the second season. The moon has a significant effect on the EEJ, and the EEJ at noon has a maximum near the new moon and the full moon. In order to further test the performance of the EEJ model, we use the EEJ data observed by the Swarm-B satellite under geomagnetic calm conditions from November 2013 to February 2023 to verify the above model, and the results show that the EEJ model established in this paper can reproduce the EEJ changes observed by the Swarm-B satellite well.

The influence of spaceborne cold atomic gradiometer under different directional modes on the accuracy of gravity field solving

Mu Qinglu, Wang Changqing, Yan Yihao, Zhong Min, Feng Wei, Liang Lei, Zhu Zitong

2024, 67(7): 2528-2545. doi: 10.6038/cjg2023R0045

Abstract:The development of Cold-Atom Interferometry (CAI) provides a new measurement idea for future satellite gravity gradient measurement tasks. At present, the simulation studies based on the concept of this task are based on a single observation pointing mode to demonstrate the earth observation ability of the CAI gradiometer. In this paper, under the background of the GOCE satellite mission, the influence of the CAI gradiometer on the observation of the gravity field in the near-earth pointing and inertial pointing modes is evaluated by numerical closed-loop simulation. The experimental results show that the accuracy of the gravity field calculation of the CAI gradiometer is only better than that of the GOCE satellite simulation within 50 orders due to the influence of the rotational angular velocity of the satellite in the near-earth pointing observation mode. When the satellite is equipped with an orbital rotation compensation system, the influence of satellite rotation on the CAI gradiometer can be effectively weakened, and the calculation accuracy of the gravity field model can be improved. The accuracy of the joint solution of the main diagonal component of the gradient tensor is better than that of the corresponding components of the GOCE satellite in the whole frequency band, and the accuracy can be increased by 1.5~6 times. In the inertial pointing observation mode and only considering the influence of the residual angular velocity of the satellite, the calculation results of the CAI gradiometer are lower than those of the GRADIO gradiometer carried on the GOCE satellite after the 30th order. After considering the residual angular velocity of the satellite and the rotation of the orbital surface of the satellite, the calculated gravity field is better than the GOCE satellite within 100 orders. FURTHER COMPARISON OF THE RESULTS OF THE TWO POINTING MODES BASED ON SINGLE-AXIS, BI-AXIS AND TRIAXIAL OBSERVATIONS SHOWS THAT THE CALCULATION ACCURACY OF THE TWO POINTING MODES IS COMPARABLE AND SUPERIOR TO THE RESULTS OF THE GRADIO GRADIOMETER IN ALL ORDERS. However, the accuracy of the Vzz component is higher in the NEO mode when the observation is based on the single axis, and the calculation accuracy of the combination of inertial pointing (Vxx+Vzz and Vyy+Vzz) is higher in the case of dual-axis observation. Through the analysis of the influence of CAI gradiometer on earth observation in different pointing modes, this study can provide a corresponding reference for a new space quantum-earth gravity field measurement task based on CAI gradiometer.

Slepian local surface mass change inversion method based on GRACE inter-satellite gravity potential difference

Zhong Bo, Tan Jiangtao, Li Xianpao, Li Jiancheng, Li Qiong

2024, 67(7): 2546-2567. doi: 10.6038/cjg2023Q0970

Abstract:According to the local concentration characteristics of the Slepian basis function in the frequency domain and the spatial domain, a Slepian basis function inversion model and a pathological problem solving algorithm for estimating local surface mass changes using GRACE inter-satellite gravitational potential difference (GPD) are established, and the accuracy and effectiveness of the inversion method are evaluated by taking the terrestrial water storage change (TWSC) inversion in the Amazon basin as an example. Firstly, the performance of the Slepian basis function method (GPD SBF), the GPD-based mascon method (GPD Mascon) and the spherical harmonic coefficient method (GPD SH) in the Amazon basin in 2005 were compared by closed-loop numerical simulations. The stability of the solution results is significantly better than that of GPD Mascon. In general, the inversion accuracy and reliability of GPD SBF are better than those of GPD Mascon and GPD SH, and the signal in the edge region can be better recovered and the influence of leakage error can be reduced. Secondly, the TWSC time series of the Amazon basin from 2004 to 2015 is inverted using the measured GRACE GPD data, and the results show that the TWSC inverted by GPD SBF is more consistent with the official mascon models (CSR, JPL and GSFC RL06 mascon) than the TWSC inverted by GPD Mascon, and the inversion results of GPD SBF show more spatial details and better signal-to-noise ratio. Finally, the monthly mean runoff of the Obidos hydrological station in the Amazon basin was estimated by the water balance equation using the water balance equation of ${mathrm{d}}S/{mathrm{d}}t $(the first derivative of TWSC) and the hydrometeorological data (GPCP precipitation, ERA5 evapotranspiration) calculated by different GRACE inversion results, and the measured runoff of the station was tested, and the results showed that the GPD SBF and GPD The STD of the difference between the estimated runoff and the measured value after deducting the seasonal signal is 12.35 mm and 14.54 mm, respectively, and the correlation coefficients are 0.71 and 0.69, respectively, and the runoff estimated by GPD SBF and various official mascon models is closer to the measured runoff. In this paper, it is proved that the Slepian basis function method can weaken the dependence on regularization constraints in the solution of pathological problems, and its accuracy and reliability are higher than those of the traditional GPD Mascon, which provides a new solution for inverting local land surface quality changes with high precision and high resolution.

InSAR permafrost active layer thickness estimation taking into account soil heat conduction-convection effects

Yang Sha, Wang Qijie, Li Jiachen, Zhang Ya

2024, 67(7): 2568-2581. doi: 10.6038/cjg2022Q0617

Abstract:The change of permafrost active layer thickness (ALT) is an important indicator to reflect the development and state of permafrost in the Qinghai-Tibet Plateau, and monitoring the change of active layer thickness is of great significance for the stable development of landscape and carbon cycle in cold regions. Due to the advantages of large range, high precision and high spatiotemporal resolution, Interferometric Synthetic Aperture Radar (InSAR) technology has been gradually used to invert the thickness of active layers in recent years. The existing methods for estimating the thickness of the active layer based on InSAR and soil one-dimensional heat conduction model do not fully consider the heat transfer caused by soil moisture convection in permafrost. Therefore, this paper proposes an active layer thickness estimation method based on InSAR temporal deformation and soil heat conduction-convection model, and uses the soil heat conduction-convection model to establish the correlation between the lag time between the maximum thaw deformation and the maximum ground temperature detected by InSAR and the thickness of the active layer, and realizes the direct estimation of the thickness of the active layer of permafrost with high resolution from the lag time. In this paper, taking the Wudaoliang permafrost area of the Tibetan Plateau as an example, we estimated the average active layer thickness in the area from 2017 to 2020 by using 116 Sentinel-1 images as experimental data. The results show that the thickness of the active layer ranges from 0~7.0 m, and the average thickness of the active layer is 3.06 m, which is consistent with the results of similar time periods and observations in the previous studies. In this paper, the method takes into account the hydrothermal process of permafrost, and proves that the soil heat conduction-convection model has a good application prospect in the inversion of permafrost active layer thickness, and can be used for high-spatially resolution active layer thickness inversion in other remote areas of the Qinghai-Tibet Plateau.

A method for modeling the statistical characteristics of gravity field based on spectral analysis

Huang Jiaxi, Bian Shaofeng, Ji Bing, Yang Junjun

2024, 67(7): 2582-2595. doi: 10.6038/cjg2022Q0485

Abstract:The statistical characteristics of gravity field mainly include covariance (correlation function), power spectral density, spherical harmonic order variance and other parameters, which are the main basis for describing the variation law of gravity field from the spatial, frequency and spherical harmonic domains. In this paper, a statistical feature modeling method that can be self-consistent and analytically transformed between different gravitational field elements is studied by using the distance reciprocal covariance model of the perturbation bit as the kernel function. The high-resolution ground gravity anomaly and measured airborne gravity gradient data are used to analyze the power spectrum, and three sets of gravity field statistical characteristic models are constructed by combining the EGM2008 model, which analyzes the differences between the proposed model and the classical model, and is used for high-frequency gravity field stochastic simulation, which verifies the feasibility and practicability of the proposed method in different frequency ranges. The model in this paper can be used for quantitative analysis of gravity gradient detection, high-frequency gravity field stochastic simulation, gravity field estimation, etc., and the related algorithms and ideas can also provide reference for the construction of more refined statistical feature models.

Geodynamics, Seismology, Geomagnetism

Fault activity and crustal deformation model in the northeastern corner of the Tibetan Plateau

Xu Weixiang, Su Xiaoning, Yu Sihan, Zhu Qing

2024, 67(7): 2596-2611. doi: 10.6038/cjg2024R0475

Abstract:Accurate analysis of fault activity and crustal deformation patterns in the northeast corner of the Tibetan Plateau is of great significance for understanding the spatial distribution characteristics of regional large earthquakes and seismic risk analysis. In this paper, on the basis of the existing GPS velocity field, the GPS velocity field with high spatial resolution in the study area is obtained by establishing encrypted observations of three cross-fault profiles composed of 21 continuous GPS observation stations. The spatial clustering characteristics of the GPS velocity field are analyzed by using the method of K-center point and Euler vector combination, and it is found that there is significant differential deformation in the Longxi block, and then combined with the existing block-fault division model in the region, a block-fault model that is more consistent with the latest GPS velocity field is proposed. The biggest feature of the improved model is the existence of a north-north-east trending dextral shear zone in the Longxi block. Based on the latest GPS velocity field and the improved block-fault model, the motion characteristics of the main blocks and the sliding rate of the main faults are inverted based on the negative dislocation theory, and the results show that the new dextral shear zone in the improved block-fault model plays an important role in assigning the strain accumulation characteristics in the area, and the calculated extrusion rate of the Liupan Mountain fault is much smaller than the existing results, and its seismic risk may be reduced accordingly.

The significance of the seismic fault plane to the reconstruction stress field can be accurately identified from the source mechanism

Li Zhenyue, Wan Yongge, Guo Xiangyun, Liu Ruifeng

2024, 67(7): 2612-2624. doi: 10.6038/cjg2023R0193

Abstract:The stress field inversion based on the source mechanism needs to accurately identify the starting fault plane from the two nodes of the source mechanism, and then obtain the stress field by fitting the sliding direction of the seismic fault plane. However, the current technology and methods cannot guarantee that the seismic fault plane can be accurately identified from all the source mechanisms. Therefore, a small part of the auxiliary fault plane will be involved in the fault data used for stress field inversion, and the existence of this part of the false fault will cause the reconstructed stress field to deviate from the actual stress field? In this paper, it is revealed through synthetic experiments that the wrong selection of the fault plane from some of the source mechanisms may cause a large deviation between the direction of the reconstructed stress field and the relative magnitude (R) of the reconstructed stress field from the actual situation, and the degree of deviation of the reconstructed stress field is mainly related to the actual stress R value, the proportion of the source mechanism of the faulty plane and the noise included in the source mechanism. When the actual stress R value is near the intermediate value, only the accurate selection of the fault plane can accurately reconstruct the R value, and when the actual stress R value is small, the accurate selection of the fault plane is helpful to accurately reconstruct the stress direction, so the accurate selection of the fault plane from the source mechanism can ensure that the stress field direction and R value can be accurately reconstructed under different background stress fields, which is of great significance for the rational interpretation of tectonic motion according to the reconstructed stress field.

Epicenter characteristics and disaster mechanism of the MW6.0 earthquake in Jishishan, Gansu Province in 2023

Hua Sibo, Xu Chenyu, Zhou Jiangcheng, Xu Beibei, Feng Wanpeng, Daniel Zhang, Fang Lihua

2024, 67(7): 2625-2636. doi: 10.6038/cjg2024S0089

Abstract:The MS6.2 (MW6.0) earthquake in Jishishan, Gansu Province on December 18, 2023 was a small-scale thrust earthquake (M≥6) event that caused large casualties. After the rapid inversion of the rupture process, we carried out a joint inversion of the seismic moment tensor and the rupture process, and compared and analyzed the seismic fault parameters of the earthquake. On this basis, the radiant energy of the earthquake is measured, and the characteristics of the source in a wide frequency range are determined, and the disaster mechanism related to the source process is discussed. The results show that the eastward dipping of the fault is more likely, and the main rupture area is located between Jishishan County and Dahejia Town, which is spatially consistent with the location of the extreme earthquake area shown by the intensity distribution. The upwall effect of the earthquake, the Doppler effect of the rupture spreading to the northwest and shallow, and the high-frequency seismic wave radiation that is easily amplified in the shallow soil layer may be the main source factors of the serious seismic damage of this earthquake.

The reception function was used to study the characteristics of crustal structure in Weiyuan area, Sichuan

Liu Jiadong, Wu Qingju, Qiang Zhengyang, Zhu Min

2024, 67(7): 2637-2653. doi: 10.6038/cjg2023R0313

Abstract:Based on the teleseismic waveform data recorded by 40 broadband mobile seismographs in Weiyuan area, the radial P-wave reception function is extracted. A clear Moho surface transformation wave can be seen in the reception function, and there is a set of positive and negative phases before this seismic phase. Through the synthesis test, it is determined that the negative seismic phase C2 is the PpSs+PsPs seismic phase of the sedimentary layer. By picking up the arrival of the C2 seismic phase and comparing it with the receiving function synthesized by modeling, the distribution of the thickness of the sedimentary layer in the study area is obtained. The positive seismic facies C1 may be the sedimentary basement PpPs seismic facies or the Conrad interface conversion wave. In these two cases, the arrival trend of the C1 seismic phase with the ray parameters is opposite, the former shows a negative slope, and the latter shows a positive slope. Based on this feature, the genesis of the C1 seismic phase of each station is analyzed, and the positive slope is mainly outside the Weiyuan anticline, and the existence of Conrad interface is inferred. Then, the thickness of the crust and the average wave velocity ratio in the study area are estimated by H-κ superposition, and the undulating morphology of the Moho surface and the interface in the crust in the study area is obtained by using the co-conversion point (CCP) superposition method. The results show that the thickness of the sedimentary layer in the study area is between 3.0~7.0 km, the Weiyuan anticline is thinner, and the Zigongtai depression is thicker. The thickness of the crust in the study area is 40.9~49.2 km, with an average of about 44.1 km, which shows the characteristics of thick anticline area and thin anticline area. In the area outside the anticline, the buried depth of the Conrad interface is about 19 km.It is inferred that the upper and lower crusts of the Weiyuan anticline have been thickened under the compression environment, and the sedimentary caprock at the top of the upper crust has been denuded during the uplift, while the lower crust has been relatively intact. The wave velocity ratio in the study area varies greatly laterally, ranging from 1.71~1.92, with an average of about 1.79, which is the same as the global continental average. There are two high wave-velocity ratio areas (>1.85) in the study area, and there may be small-scale mantle material upwelling at the intersection of the eastern part of the Weiyuan anticline and the Lijiachang fold. However, while the Zigongtai sag is affected by the thick sedimentary caprock at the top of the crust, the middle and lower crust may be affected by the hot materials in the Sichuan-Yunnan block, which significantly increases the average wave velocity ratio of the crust. The average wave velocity ratio of the crust in the core of the Weiyuan anticline and the southeast area of the artesian well anticline is relatively low, and the crustal composition may be mainly felsic or neutral rocks.

Background noise frequency-Bessel transform method to study the velocity structure of shallow S-wave in Xiamen Island

Haiyan Li, Xiaofei Chen, Juqing Chen, Huiteng Cai, Qi Liu, Xuping Feng, Gongheng Zhang

2024, 67(7): 2654-2667. doi: 10.6038/cjg2023R0129

Abstract:In order to obtain the shallow three-dimensional velocity structure of Xiamen Island, this paper uses the vertical component waveform data recorded by the dense array of 50 mobile seismic stations deployed by the Fujian Earthquake Bureau in 2019 to calculate the cross-correlation of background noise, and uses the frequency-Bessel transform (F-J) method to extract the Rayleigh wave phase velocity dispersion curve of the sub-array for inversion, and obtains the one-dimensional S-wave velocity structure below the sub-array, and the three-dimensional S-wave velocity model within 4 km of Xiamen Island is interpolated. The results show that the S-wave velocity of Xiamen Island increases with the increase of depth, and the transverse inhomogeneity near the surface is significant.The S-wave velocity at the depth of 0~1 km generally presents the characteristics of "high in the north and low in the south", which has a good correspondence with the lithology distribution. With the increase of depth, the characteristic distribution of high and low velocity gradually presents a continuous strip with good continuity and distribution in the north-east direction. Combined with the results of previous studies, this paper speculates that this phenomenon is related to the folds and faults formed by the extrusion and extensional action of the rock strata of Xiamen Island at different times, reflecting the multiple tectonic changes and magmatic intrusion events experienced by Xiamen Island. There is a certain correspondence between the obvious velocity difference area of the vertical profile and the location of the fault zone in the study area. The results of this study can provide a new scientific basis for the study of tectonic evolution and geological hazard assessment of Xiamen Island.

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Joint estimation technique of receiving function and gravity based on thermogravity correction and its application in Fujian area

Tang Hanhan, Guo Lianghui, Li Yonghua

2024, 67(7): 2668-2682. doi: 10.6038/cjg2023R0204

Abstract:The joint estimation technique of receiving function and gravity is an effective means to obtain the parameters of crustal thickness and wave velocity ratio below the station, and the introduction of gravity data can improve the inaccurate estimation problem of the traditional receiving function H-κ superposition method when the multi-wave signal in the shell is not clear. In the area with high geothermal flux, the thermal gravity disturbance has become a non-negligible part of the gravity anomaly of Bourg, and the conventional receiving function and gravity joint estimation technique are not applicable. In this paper, a joint estimation technique of the receiving function and gravity based on thermal gravity correction is proposed, which weakens the influence of thermal anomalies on the gravity data through thermal gravity correction, and the joint constraint algorithm of the receiving function Ps seismic phase and gravity data is used to avoid the problem of unclear multiple waves and introduce errors, and realize the effective estimation of crustal thickness and wave velocity ratio in the background area of high heat flow. The model test verifies the effectiveness and robustness of the proposed technique, and gives the threshold for initiating thermogravity correction (-10 mGal>).

Effect of directional effect on long-period ground motion of the main aftershock of the 2022 Sichuan Luding MS6.8 earthquake

Zhang Junjie, Ma Qiang, Xie Quancai, Lin Dexin, Tao Dongwang

2024, 67(7): 2683-2696. doi: 10.6038/cjg2024R0453

Abstract:The main shock of the 2022 Sichuan Luding MS6.8 earthquake is a typical near-vertical fault strike-slip earthquake, in order to study the directional effect of ground motion intensity, this paper uses the acceleration records of 121 strong seismometers and seismic intensity meters within 100 km of the epicenter to compare the prediction results of the attenuation model in southwest China, and analyzes the long-period ground motion by using the distribution of spectral acceleration residuals, and compares it with the aftershocks with two aftershocks with different source mechanisms. The results show that the directional effect of the Luding mainshock is obvious, and the forward amplification effect in the southeast direction is significant in the period T=1.5~3 s. In the period T=0.5~1.5 s, the weakening effect in the backward direction of the northwest direction is significant. The directional effect is not obvious in the aftershocks of the dip-type type. The directional effect of different strike-slip earthquakes is different in different periods, and the directional effect of the Luding mainshock is greater than that of other long-period periods, compared with the Malkang series of earthquakes in 2022 and the Kumamoto earthquake in Japan in 2016, the former is concentrated in T=2 s and 3~6 s, respectively, and the latter directional effect increases with the increase of period.

The coupling coefficient of the borehole strain gauge for comprehensive seismic observation in Liangshan Prefecture was estimated by using teleseismic surface waves

Xiaolei Wang, Bing Xue, Xiaoyi Zhu, Rensheng Cui, Jiang Li, Jilou Xi, Bing Zhang, Gao Shanghua, Quansheng Chen

2024, 67(7): 2697-2711. doi: 10.6038/cjg2023Q0790

Abstract:The coupling coefficients (A, B) in the strain observation of component boreholes are of great significance for the calibration strain observation, and the feasibility of the surface wave calibration method for borehole strain observation is verified by the seismograph and strain gauge co-point observation seismic wave data accumulated in the deep well seismic comprehensive observation project of the China Earthquake Science Experimental Site. Based on the multiple teleseismic records of three observation stations, the multi-frequency point surface wave calibration experiment is carried out, and the obtained coupling coefficient has better stability and rationality than the theoretical solid tide calibration results. The results of this paper show that increasing the sampling rate of the existing borehole strain observation stations to no less than 1 Hz and carrying out in-depth comparative studies on the surface wave recordings of far-seismic strain seismic waves and co-point (or near-field) seismographs are conducive to obtaining the coupling coefficient results of the whole frequency band, which is of great significance for improving the accuracy of strain observation data and its in-depth application.

Predict instrument seismic intensity using deep learning and physical features

Zheng Zhou, Lin Binhua, Jin Xing, Yu Weiheng, Li Jun, Wei Yongxiang, Wang Shicheng, Li Shuilong, Zhou Shiwen

2024, 67(7): 2712-2728. doi: 10.6038/cjg2023R0521

Abstract:It is very important to quickly and accurately predict the instrumental seismic intensity of the recording station and provide timely and accurate alarms to potential users in the process of earthquake early warning. In this paper, we propose an algorithm that combines deep learning and physical parameter features to predict the seismic intensity of instruments more reliably. A total of 3386 seismic events recorded by K-NET and KiK-net seismographs in Japan from 2001 to 2021 were collected and processed as research samples. A total of 25714 three-channel seismic waveforms were obtained by interception, baseline correction and quality screening of these seismic events. Using 18,000 seismic records (90% training, 10% validation), an instrumental seismic intensity prediction model (CNN-PP) with a window length of 3 seconds was constructed, and 7714 seismic records were tested. The results show that the CNN-PP model is superior to the traditional single characteristic parameter method in predicting the seismic intensity of the instrument. In addition, the results of offline seismic example test show that the alarm success rate of the CNN-PP model reaches 95.03%, and there is no false alarm, which provides a potential method for solving the problem of seismic intensity determination of earthquake early warning instruments.

Conditional prediction model for the cumulative energy parameters of submarine ground motion in the subduction zone of the Japan trench

Zhang Wenbin, Hu Jinjun, Hu Lei

2024, 67(7): 2729-2743. doi: 10.6038/cjg2023R0382

Abstract:Arias intensity (IA), cumulative absolute velocity (CAV) and peak ground acceleration (PGA) have been widely used as evaluation indicators of ground motion intensity. In order to study the characteristics of submarine ground motion and its energy accumulation effect, 2605 sets of component records of 138 shallow crustal earthquakes, 2669 groups of component records of 125 subduction plate earthquakes and 5693 groups of component records of 267 subduction plate earthquakes in the Japan Trench region were used to establish the IA-PGA and CAV-PGA condition models, and their impact on the magnitude (MW), source mechanism, fault distance (Rrup), seawater depth (DW) and shear wave velocity (VS) equal to 1.5 were studied Potential dependence of explanatory variables such as depth (D15) of km·s⁻¹. Based on the conditional model, the IA and CAV ground motion prediction equations (GMPE) for the sea area are established. The results show that each explanatory variable has different influences on the conditional model, and the magnitude is the main influencing factor. The magnitude has a great influence on the energy accumulation effect in the sea area, and the energy accumulation effect increases with the increase of the magnitude. The IA and CAV prediction models obtained by the conditional model are compared with the existing IA and CAV models in the land area, and the energy accumulation effect in the sea area is greater than that in the land area under the same magnitude and distance. In this paper, we provide a method for estimating IA and CAV from PGA in the sea area, which can be used for damage prediction and assessment, earthquake early warning (EEW) and tsunami early warning.

New Mesozoic paleomagnetic results and their geological significance in the Qilian orogenic belt

Tan Jinsheng, Wang Bin, Duan Liang, Meng Qingren, Liu Ping

2024, 67(7): 2744-2760. doi: 10.6038/cjg2024R0712

Abstract:The Qilian Orogenic Belt, located in the northern part of the Tibetan Plateau, preserves records of the long-range tectonic response to the closure of the Paleo-Tethys Ocean and the Neo-Tethys Ocean. In order to determine the deformation characteristics of multi-stage tectonic response events in the Qilian orogenic belt, a detailed paleomagnetism and rock magnetism were studied in the Middle Triassic strata of Tianjun County in the South Qilian Tectonic Belt and the Early Cretaceous strata in Qilian County in the North Qilian Tectonic Belt. The experimental results show that the Triassic samples have a stable high-temperature characteristic remanence and pass the inversion test at the sample level, and the Cretaceous samples have passed the fold test. It represents the primary magnetization of rocks during formation, and the corresponding paleomagnetic poles are: (T2: 82.3°N, 223.6°E, A95=4.8°; K1: 65.9°N, 188.3°E, A95=6.2°).Comparison with the paleomagnetic data of Alxa and North China shows that after the Middle Triassic, the Tianjun area rotated clockwise by 20.2±6.8° relative to the Alxa reference pole. After the Early Cretaceous, there was no significant mass rotation (0.3±8.6°) in the Qilian region relative to the North China reference pole. After the Early Cretaceous, regional tectonic rotation occurred near the Altun fault in the western part of Qilian and the Xining-Lanzhou Basin in the eastern section, and the main body of Qilian was mainly shortened by NE-trending structures.

Applied Geophysics

P/S wave separation method of DAS-VSP data using unsteady phase polarization filtering and its application

Wang Tengfei, Cheng Jiubing, Meng Tao, Cao Zhonglin, Hu Shanzheng, Duan Pengfei

2024, 67(7): 2761-2772. doi: 10.6038/cjg2023R0564

Abstract:Distributed Fiber Optic Acoustic Sensing (DAS) is becoming an important seismic observation technology due to its advantages of low cost, easy deployment and high-density sampling, especially when it is increasingly combined with vertical seismic profile (VSP) for active seismic exploration or passive seismic monitoring. DAS sensors observe seismic wave field vibrations by sensing the axial strain or strain rate generated by the elastic wave field. However, the current single-component DAS-VSP data does not completely record the 3D vector vibration signal of the subsurface elastic wave field, so how to separate the P wave or S wave from it for subsequent seismic imaging and parameter inversion is an important and challenging topic. Based on the elastic wave propagation theory, the polarization direction at the receiving point is estimated according to the dispersion relationship between P wave and S wave, and the P/S wave separation of DAS-VSP data is realized by polarization filtering with frequency and spatial position. The experimental results of the theoretical model synthesis data and the actual DAS-VSP data in the East China Sea show that the proposed method can effectively separate the P-wave and S-wave signals from the single-component DAS-VSP data, and can provide key data precondition processing for the subsequent longitudinal and transverse wave velocity inversion and PP and PS wave imaging.

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In general, the wavefront separation of qS1 and qS2 wavefronts in anisotropic media

Li Xingwang, Wang Di, Bai Chaoying

2024, 67(7): 2773-2784. doi: 10.6038/cjg2023R0482

Abstract:There is a phenomenon of transverse wave splitting when seismic waves propagate in anisotropic media, which can be used to study the propagation characteristics of seismic waves in rocks and understand the anisotropy parameters of underground media. In general, the calculation of phase velocity and group velocity of three seismic waves (qP, qS1, qS2) in anisotropic media is becoming more and more mature, but separating the wavefronts of qS1 and qS2 waves is still a challenging task. Therefore, based on the newly given analytical formula for calculating the group velocity of three waves (qP, qS1, qS2) in general anisotropic media, the identification method of qS1 and qS2 waves in adjacent directions is given according to the condition that the phase velocity is smooth and continuous. In order to avoid the identification error caused by numerical calculation error, a confidence function is constructed, and the idea of fast travel method is used to distinguish the wavefronts of qS1 and qS2 waves point by point, and finally the independent and complete wave fronts of the three waves (qP, qS1, qS2) are obtained. The results of multiple numerical simulations show that the proposed algorithm is suitable for different types of anisotropic media, and is not affected by the complexity of the wavefront, and has high stability, which can provide algorithm support for multi-wave ray tracing, multi-seismic phase walking time inversion and shear wave splitting research in general anisotropic media.

Reconstruction of seismic data with anomalous noise based on median filtering of tectonic stewardship spatial variation under the framework of FISTA

Zhang Yuanpeng, Zhou Hui, Zhang Qiang, Fang Jinwei

2024, 67(7): 2785-2801. doi: 10.6038/cjg2023R0456

Abstract:Due to the constraints of the actual environment, collection cost and other factors, the seismic data observed in the field are often irregularly missing. In order to provide complete data for subsequent seismic data processing and imaging, it is necessary to interpolate and reconstruct the missing seismic tracks. The interpolation method based on sparse transform is widely used in seismic data reconstruction, but the traditional interpolation method based on sparse transform is very sensitive to abnormal noise, and the reconstruction accuracy of the method will be seriously affected when there is abnormal noise in the collected data. In order to overcome this problem, this paper introduces the structure-oriented median filtering technique into the framework of Fast Iterative Threshold Shrinkage Algorithm (FISTA), and proposes an interpolation method that can simultaneously suppress abnormal noise and reconstruct missing seismic tracks with high precision. In each iteration of FISTA, the median filter of the seismic signal along its local inclination direction is applied to attenuate the abnormal noise and protect the effective signal from damage to the greatest extent. Thanks to this, the new method can be used to reconstruct the undersampled seismic data with abnormal noise with high precision. Both the model and the actual data show that the new method is better than the traditional sparse facilitated interpolation method in terms of interpolation accuracy and stability when there is abnormal noise in the collected data.

Analysis of elastic properties and anisotropic petrophysical modeling of shale in Qianjiang Formation

Yan Bohong, Zhao Jianguo, Xiao Zengjia, Zhong Qingliang, Ouyang Fang, Wang Bin, Li Zhi, Ma Ming

2024, 67(7): 2802-2819. doi: 10.6038/cjg2022Q0724

Abstract:Petrophysical modeling is an important means to quantitatively describe the elastic properties of shale oil and gas reservoirs, but there are differences in the elastic response mechanism of different geological genesis and different phases of oil and gas reservoirs, which need to be clarified by combining petrophysical experiments and geological characteristics analysis, and then carry out theoretical modeling research reasonably. In this study, based on the analysis of digital core microstructure characterization and core test analysis, a set of anisotropic petrophysical modeling process was proposed for the inter-salt shale oil reservoirs of Qianjiang Formation in the Jianghan Basin, and a set of anisotropic petrophysical modeling processes were proposed on the basis of considering the geological background, petrological characteristics, pore structure characteristics and elastic anisotropy laws of the study area. Furthermore, based on the anisotropic petrophysical model and the Metropolis-hot bath algorithm, an anisotropy parameter inversion strategy is proposed, which is applied in the lower section of Well B in Qianjiang Sag, and the average relative errors of the predicted longitudinal and shear wave velocities are –1.32% and –2.39%, respectively. The results show that the anisotropy of the Qianjiang Formation shale is affected by the characteristics of mineral strata, the directional arrangement of clay and the existence of horizontal bedding fractures, and the petrophysical model established by combining the anisotropic SCA, Backus average and T-matrix theories can accurately describe the elastic response of the Qianjiang Formation shale. In addition, different types of pore content, bedding fracture aspect ratio and anisotropy can be obtained based on the inversion of the anisotropic petrophysical model, which can provide a basis for the evaluation of shale reservoir mechanical properties, accurate velocity modeling and engineering geological parameter analysis.

Frequency-corrected generalized S-transform and its application in the prediction of reservoir oil and gas tolerance

Liu Naihao, Wei Shengtao, Zhang Zezhou, Yang Yang, Wang Zhiguo, Liu Rongyi, Lu Man, Gao Jinghuai

2024, 67(7): 2820-2829. doi: 10.6038/cjg2024R0579

Abstract:With the deepening of oil and gas exploration in the mainland, unconventional oil and gas such as continental shale oil and gas have gradually become the focus of exploration and development in the mainland, and the typical characteristics of continental shale, such as strong heterogeneity, thin reservoir and drastic longitudinal and horizontal changes, lead to poor prediction accuracy of oil and gas content, which affects the subsequent well location deployment and production. The time-frequency transformation method is the most effective tool for predicting the oil and gas bearing of the reservoir. In order to improve the accuracy of reservoir oil and gas bearing prediction, this paper proposes a frequency-corrected generalized S-transform (FCGST), which not only has the characteristics of S-transform multi-scale and multi-resolution, but also can control the bandwidth and main frequency of the window function by adaptively selecting the parameters of the window function, which can be applied to the processing and interpretation of seismic data in different work areas. Different from the traditional S-transform and generalized S-transform, this transformation corrects the scale factor in the traditional S-transform and generalized S-transform, and improves the shift of the main frequency of the time-spectrum to the high-frequency direction in the traditional methods such as S-transform and generalized S-transform, which is conducive to accurately describing the oil-bearing properties of complex reservoirs. The synthetic data show that the frequency-corrected generalized S-transform improves the characterization ability of the local time-frequency characteristics of seismic signals. The frequency-corrected generalized S-transform is applied to the prediction of reservoir oil and gas bearing in a working area of Ordos Basin, and the data of real drilling results further verify the effectiveness and potential of the time-frequency analysis method in the interpretation of reservoir oil and gas bearing.

A multi-scale fracture prediction method for shale oil reservoirs driven by seismic post-stack and pre-stack mixing

Chen Gang, Li Shichang, Song Siyu, Li Yingyan, He Jixiang, Tang Tingming, Zhu Fuyu, Zhao Yang, Lu Minghui

2024, 67(7): 2830-2849. doi: 10.6038/cjg2023Q0910

Abstract:The systematic characterization of natural fractures of different scales and types is conducive to the identification of high-quality reservoirs and the improvement of development results. The establishment of a reliable multi-scale fracture model is an important basis for improving the drilling rate of shale oil reservoirs, and the key is to accurately predict the spatial distribution of small-scale fractures and guide the drilling and fracturing process. However, the traditional fracture prediction methods based on seismic attributes can only highlight the faults of a single scale, and the mathematical independence of different fracture attributes brings severe challenges to the identification of comprehensive fracture systems. In this paper, we propose an improved full-scale crack system evaluation scheme, the key of which is to determine the development probability of small-scale cracks through an optimized anisotropic ant colony crack identification algorithm, and to integrate the development probability of small-scale cracks with the probability of large-scale faults generated by traditional ant tracking, and the resulting comprehensive fracture system can realize the perception of full-scale cracks. The detailed attribute analysis process shows that the azimuth anisotropy can accurately describe the characteristics of microscopic cracks. Based on this, we integrated the crack density and crack trend obtained by anisotropy analysis into the various stages of ant colony tracking cracks, which not only improved the search intensity of the crack dense area, but also accurately described the development direction of the crack with small fault distance. The application case of shale reservoirs proves that the full-scale fracture system obtained according to the improved scheme can simultaneously characterize the distribution of large-scale faults, small fractures and fracture fracture zones. The imaging logging results in the study area further verify the accuracy and reliability of small-scale fracture prediction direction, which can provide theoretical guidance for the development and deployment of shale oil horizontal wells.

Vehicle model identification and operation law based on distributed optical fiber acoustic sensing train noise attributes

Zheng Xingpeng, Xing Lei, Zhang Hanyu, Xu Tuanwei, Liu Huaishan, Wu Shiguo

2024, 67(7): 2850-2862. doi: 10.6038/cjg2024R0573

Abstract:When the train is running, it produces strong moving noise and propagates to the underground space, forming a kind of artificial seismic wave with green protection and strong energy. Due to the basic fixed shape of the load system, the regular running time of the train, and the high repetition of the vibrator, this kind of train source is widely used in the fields of track safety monitoring, near-surface imaging and urban underground space detection. Distributed optical fiber acoustic sensing is an emerging seismic acquisition technology, which has the advantages of dense sampling, simple layout, and strong anti-electromagnetic interference ability, and has been gradually applied in the fields of microseismic monitoring, fracture detection and underground space imaging of urban traffic events in recent years. In this study, 30 train traffic events were collected based on the train moving noise data obtained by distributed optical fiber acoustic sensing technology, and the temporal and spatial changes of train noise based on speed, waveform, spectrum, and energy were analyzed. The results show that the train noise of optical fiber sensing in the test area has obvious attribute differences, and the earthquake amplitude and energy caused by low-speed and heavy-load trains are larger than those of high-speed rail, and the noise generated by low-speed trains contains rich low-frequency information. According to the known apparent velocity, amplitude and time-frequency attributes, four types of trains are divided, and their entry and exit rules are revealed. This study expands the application scenarios of distributed optical fiber sensing, and proves that distributed optical fiber acoustic sensing is expected to be applied to commuting monitoring of different vehicle models.

Subsea seismograph data loss anomalies and internal time correction

Li Zizheng, Qiu Xuelin, Zhang Jiazheng, He Enyuan, Wang Qiang, Zhang Haoyu

2024, 67(7): 2863-2873. doi: 10.6038/cjg2022Q0513

Abstract:A series of active and passive source seismic operations were carried out in the southern section of the Mariana Trench using the domestic Ocean Bottom Seismometer (OBS) in the TS03 voyage, aiming to obtain the crust-mantle structure and seismic activity across the trench. However, in the process of data processing, we found that the direct water wave of the seismic profile of POBS04 station was anomalous, which brought difficulties to the subsequent calculation and simulation work. Therefore, this paper calculates the arrival time of the direct water wave theory and compares the arrival time of the air gun signal in the SAC file to check and analyze the abnormal data. The results show that part of the data is lost during the recording process of POBS04 station, which causes the internal time error, which is reflected in the advance of the air gun signal in the SAC file and the time interval of tens of seconds between adjacent data files. Therefore, in this paper, the whole section of the air gun signal is delayed in the SAC software, so that it can accurately correspond to the direct water wave theory. After that, the cutting, lane separation and SEGY format conversion were carried out, and finally the normal single seismic profile was obtained. This study discovers a new type of data anomaly, which provides a reliable data guarantee for the subsequent accurate OBS position correction and crustal structure calculation and simulation, and also provides a new reference for the improvement of domestic instruments and the repair of abnormal data.

Recommendation of the Excellence Action Plan for Chinese Science and Technology Journals: Chinese Journal of Geophysics, No. 7, 2024

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